CS102 · Chapter 8 · Annotated SlidesMultidimensional Arrays
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Overview

Multidimensional Arrays

Declaring and creating 2D arrays, initializers, lengths, ragged arrays, the processing loops (input, random, print, sum, column sums), passing 2D arrays to methods, and 3D arrays.

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Every original slide is shown unchanged. Yellow marks on a slide point to a numbered note: hover or tap a mark to jump to its note, and hover a note to see its marks. Questions tagged Past exam appeared on a real paper; Prediction questions are likely angles, not confirmed. Pick an answer to each question: a wrong pick tells you why it is wrong, so you can try again.

All 20 slides
  1. 1 Multidimensional Arrays
  2. 2 Motivations
  3. 3 Motivations
  4. 4 Declare/Create Two-dimensional Arrays
  5. 5 Declaring Variables of Two- dimensional Arrays and Creating Two-dimensional Arrays
  6. 6 Two-dimensional Array Illustration
  7. 7 Declaring, Creating, and Initializing Using Shorthand Notations
  8. 8 Lengths of Two-dimensional Arrays
  9. 9 Lengths of Two-dimensional Arrays, cont.
  10. 10 Ragged Arrays
  11. 11 Ragged Arrays, cont.
  12. 12 Processing Two-Dimensional Arrays
  13. 13 Initializing arrays with input values
  14. 14 Initializing arrays with random values
  15. 15 Printing arrays
  16. 16 Summing all elements
  17. 17 Summing elements by column
  18. 18 Passing Tow-Dimensional Arrays to Methods
  19. 19 Multidimensional Arrays
  20. 20 Multidimensional Arrays
Slide 1 / 20

Multidimensional Arrays

Slide 1: Multidimensional Arrays
Slide 2 / 20

Motivations

Slide 2: Motivations
Slide 3 / 20

Motivations

Slide 3: Motivations
Slide 4 / 20

Declare/Create Two-dimensional Arrays

Slide 4: Declare/Create Two-dimensional Arrays

Notes

  1. int[][] matrix = new int[5][5]; matrix[0][0] = 3;

Slide 5 / 20

Declaring Variables of Two- dimensional Arrays and Creating Two-dimensional Arrays

Slide 5: Declaring Variables of Two- dimensional Arrays and Creating Two-dimensional Arrays
Slide 6 / 20

Two-dimensional Array Illustration

Slide 6: Two-dimensional Array Illustration
Slide 7 / 20

Declaring, Creating, and Initializing Using Shorthand Notations

Slide 7: Declaring, Creating, and Initializing Using Shorthand Notations
Slide 8 / 20

Lengths of Two-dimensional Arrays

Slide 8: Lengths of Two-dimensional Arrays

Notes

  1. matrix.length = number of rows; matrix[0].length = columns of row 0.

Exam angle

PredictionQ1

For int[][] m = new int[3][4];, m.length and m[0].length are:

Slide 9 / 20

Lengths of Two-dimensional Arrays, cont.

Slide 9: Lengths of Two-dimensional Arrays, cont.
Slide 10 / 20

Ragged Arrays

Slide 10: Ragged Arrays
Slide 11 / 20

Ragged Arrays, cont.

Slide 11: Ragged Arrays, cont.
Slide 12 / 20

Processing Two-Dimensional Arrays

Slide 12: Processing Two-Dimensional Arrays
Slide 13 / 20

Initializing arrays with input values

Slide 13: Initializing arrays with input values
Slide 14 / 20

Initializing arrays with random values

Slide 14: Initializing arrays with random values
Slide 15 / 20

Printing arrays

Slide 15: Printing arrays
Slide 16 / 20

Summing all elements

Slide 16: Summing all elements

Notes

  1. Sum all: nested for over rows and columns.

Slide 17 / 20

Summing elements by column

Slide 17: Summing elements by column

Notes

  1. Column sums: outer loop over columns, inner over rows.

Exam angle

PredictionQ1

Write code that sums each column of int[][] m.

Compare with the model answer

for (int c = 0; c < m[0].length; c++) { int total = 0; for (int r = 0; r < m.length; r++) total += m[r][c]; System.out.println(total); }

Slide 18 / 20

Passing Tow-Dimensional Arrays to Methods

Slide 18: Passing Tow-Dimensional Arrays to Methods

Notes

  1. Pass a 2D array: public static int sum(int[][] m).

Slide 19 / 20

Multidimensional Arrays

Slide 19: Multidimensional Arrays

Notes

  1. 3D arrays: double[][][] scores = new double[6][5][2];

Slide 20 / 20

Multidimensional Arrays

Slide 20: Multidimensional Arrays